1. Field of Invention
The invention relates to extraction apparatus and method thereof and more particularly to an apparatus of obtaining essential oils, essence, and pigments from odorous raw materials (e.g., plant materials and Chinese medicinal herbs) by microwave heating under sub-critical conditions.
2. Description of Related Art
Distillation methods are well known in the art. A type of simple distillation method is batch distillation. Drawbacks of a batch distillation are detailed below. Vapor with volatile substances may be condensed prior to leaving the extraction cartridge due to heat loss, which results an obvious temperature decrease and a lower efficiency of extraction. Further, concentration of the volatile substances in the distillate (i.e., essence) is low since it is diluted with a large volume of water.
Other extraction methods are also well known in the art. One typical extraction apparatus is Soxhlet extractor. Drawbacks of the Soxhlet extractor include time consuming, a low reproducibility, and application of organic solvents during the extracting process.
Nowadays extraction methods including ultrasonic extraction and ultra critical extraction with carbon dioxide (CO2) have been developed. Drawbacks of the ultrasonic extraction are adding of a large amount of organic solvent and time consuming during the extracting process. On the other hand, the ultra critical extraction with CO2 has defects of low energy efficiency as well as its apparatus is costly.
The latest extraction method is microwave extraction by being heated with a microwave oven because microwave heating reveals less thermal resistance effect than an electrical oven doing. Though the efficiency of microwave extraction is found higher than a batch distillation, it has been focused on heating water or organic solvents at bottom layer of microwave device to generate vapor for extraction of volatile compounds. The advantages and benefits of microwave extraction have not been fully utilized as viewed by the present inventor. Thus, the need for improvement still exists.